Hi everyone,

I have been lurking for a while but have now subscribed with the hope of tapping everyone’s knowledge for a renovation I am about to embark on. I will try not to ramble on for too long initially.
The property is a circa 17/18th century brick built coach house in Norfolk. Approx 360m2 total floor area over 3 floors (some of this will most likely be divided into a separate annexe). Currently occupied but we will be moving in at the beginning of March and will be renovating, including an overhaul of the heating system. The building has not been upgraded in many ways to improve thermal efficiency. The attic has been converted but I think it is only 50mm PIR insulation between the rafters. If any of the walls require plastering I will probably look to add SOME internal insulation in the form of something that will allow the building to breathe. I will add shutters to the windows and possibly secondary glazing in time. It currently has an old oil fired heating system.

We are a family of 4 (who like to be warm and like hot baths!). I would also say that my primary goal here is to make the house comfortable whilst decreasing its reliance on fossil fuels. If I wanted a super-efficient home, I would not have bought a 300+ year old coach house

My current plan is install UFH for the ground floor only. Most of the floors are solid but I have a little space to add SOME insulation. This will be paired with an ASHP for DHW too. I toyed with the idea of GSHP but the added work/cost put me off.

There is a wood burner, which can be used in the living room and an electric converted Aga in the kitchen. Because my wife likes to keep the house quite warm, my thought was to keep the oil fired system but upgrade the boiler with the intention of using it only when required and during deepest winter when the ASHP will not be running particularly efficiently. However, I would like to size the ashp to heat the whole house, which has been roughly calculated at 24kW.

Does this sound sensible or do i ditch the oil entirely? I will be enlisting the help of installers but I will also be doing a lot of the prep/simple work myself. The installer advised ditching the boiler, otherwise I will not be eligible for RHI payments.

By biggest current concern is that there is no point in installing UFH when I can only add minimal insulation. I have read a number of posts suggesting I would lose too much heat into the ground but the company I have consulted for installation seem to think 25mm foil faced eps will be ok! The kitchen area has a suspended floor so that should be ok but the rest of the house has solid floors which probably consist of a fairly thin screed over earth or possibly brick/stone then earth.

Should I just stick with enlarged rads? My counter to that argument is thermal comfort. Because of the way UFH heats the room, can you put less energy into the room? IE would losses to the ground be mitigated by the reduced amount of energy required to make you FEEL comfortable (rather than achieve an average temp). It is something I have not seen mentioned an awful lot yet. I have seen lots of impressive calculations about heat loss (something I need to figure out myself) but little discussion on comfort, which is altogether more subjective. For example, if you have a room that is at 20C but stone floors that are making your feet feel cold, your overall thermal comfort will be disproportionately lowered by your least comfortable body zone

...I said I wouldn’t ramble!

Here is a link to some pictures, EPC and floor plans. https://drive.google.com/drive/folders/1NltX79pqjmajWHI6V1zs4Wm1q546K3ib?usp=sharing

Thank you for that. I will definitely do some exploratory digging to see what is possible. Maybe i can find some original stone/brick to re-use! I think even if I cant dig down I will go for a minimum of 50mm insulation rather than 25m (i know this is still well below the ideal).

I had just started reading more about perimeter insulation. I will do some more research. There is a french drain on the south side (that may need some attention by now) so the ground should be ok but i know the water table is pretty high at the moment.

Actually the house is painted brick at present. I am not sure if i could get away with any EWI as it is grade 2 listed but i might be able to on the north face (main entrance) as this faces away from the hall that the Coach House originally belonged to.

I will do away with the oil boiler. I can top up the living room with the wood burner, which should help a bit with what will be the main bedroom above. I have more questions about best utilising the heat from that but i will save that for another post!

Or Hemcrete IWI if you are a real masochist. Probably better to stick with wood fibre boards!

What minimum thickness for limecrete slab and what is the thickness ratio between that and the insulation below? If i find any old stone/brick floor i will re-use it as flooring in one way or another. I think the CO may request this anyway. Yes, enlarged rads for the first and second floor. I would prefer cast iron but assume these would not be ideal for an ashp and they would be very heavy! I assembled a 30 section one in the last house i renovated and dont fancy doing that for a whole house.

I love the idea of running rads from a back boiler. I have a good supply of wood here and will be planting more suitable trees for coppicing this year. I wondered about just running a couple of rads from the wood burner, completely separate from the rest of the system. I watched a pleasing video of a very simple version of this on youtube earlier with a Salamander stove and copper kettle as header tank! https://youtu.be/idyH-3-DBIs

I think i will have to talk to the conservation officer with regards to the internal or external plaster/render. The wood fibre insulation boards look very convenient.

Do you have 3 phase electricity? Because I don't think you'll be running an ASHP of that size on a single phase.

Cast iron rads not a problem for heat - they just need to be oversized!! So bit of a problem moving them.

25mm insulation definitely not enough under UFH.

Posted By: Tomasz_PI wonder how much a 3 phase upgrade would cost.

I think the only way to find out is to ask. Costs will depend on local circumstances I think.

Posted By: Paul in Montrealwhat's the usual supply capacity in the UK?

80 A or 100 A at 230 V nominal.

Posted By: Peter_in_Hungary: “This makes electric kitchen hobs v. expensive…”

Wandering off topic a bit but nice point here about induction hobs for that sort of circumstance: https://greening.me.uk/2020/09/07/inducted-into-the-hall-of-fame/

Odd, I'm pretty sure an IKEA hob I was looking at a while ago did that but can't find one with less than a 32A supply now. Guess why I'm interested ;-). I really doubt anybody has a use for all rings on full at the same time.

Posted By: Peter_in_HungaryA single phase anything over this is charged extra per A over 32.

Similar in France; standing charges go up in steps at 15, 30, 45, 60A and beyond.

One device that may help - you many already have one - is a load-shedder (délesteur électrique) that switches off designated circuits to keep the current below the limit (stopping the supply tripping out).

Posted By: Ed DaviesOdd, I'm pretty sure an IKEA hob I was looking at a while ago did that but can't find one with less than a 32A supply now. Guess why I'm interested ;-). I really doubt anybody has a use for all rings on full at the same time.

IIRC, you're planning to be offgrid, so presumably want to be able to limit power draw. I agree that we rarely have everything on full at the same time, but we do frequently have at least a couple of the most powerful places on boost at the start of cooking to boil water or start frying etc. I found https://kitchinsider.com/13-amp-induction-hob/ and based on that would suggest the Neff looks like a good bet - one of our friends has one and likes it. Regardless I'd suggest wiring for a 45 A supply anyway and then just limiting with a fuse/circuit breaker, in the cause of anticipating future possibilities.

<blockquote><cite>Posted By: Rick_M</cite>Would the eaves need to be extended/altered if EWI was used?</blockquote>
Well spotted, you are probably right. Or at least, i would not be able to get any great thickness on there. I think i am going to have to do everything i can with what i have. Extra insulation is an area that will always present difficulties. My best hope my be getting some on the interior. I am not actually that keen on the bare brick on the inside.

I will see what the heat pump installers come back with this week. I suspect their quote will be very expensive. I am stuck in a situation where i would like to keep costs down and do a lot myself but i am time poor! I am also still waiting on the local limecrete supplier to come back with some prices?

Assuming i can dig down to earth. What layers should i use on top of that? The local supplier says the foamed glass insulation layer can go down to 80mm in some cases then the limecrete on top of that at 100mm. That seems like it should be achievable. What suggestions do people have for perimeter insulation?
https://limecrete.co.uk/wp-content/uploads/2020/04/Limecrete-Company-Cross-Section-Slabless.pdf

80mm seems very slim to me. Isn't the foamed glass used as a structural replacement for compacted type 1 under the slab? As such I would have thought 80mm is not enough. I can't remember the insulation values of expanded glass but with UFH you would want to get more than what that offers I would think.

Posted By: Dominic CooneyYour dig out might be limited by the depth of the foundations, you shouldn't dig out lower than them.

You will need an engineer who understands your soil conditions to be sure, but commonly it's said you can dig down further at 45° from the walls, so the centre of the room can be somewhat deeper.

<blockquote><cite>Posted By: Tomasz_P</cite>The local supplier says the foamed glass insulation layer can go down to 80mm</blockquote>

I used Foamed glass (Perinsul T4+ I think) - it was 100mm thick, and I put it all the way down to the top of foundations (~700mm down), and up to DPC. I covered it with fake slate (Cement fibreboard). EWI above DPC is 150mm, so there's a 50mm step. Probably could've gone thicker than 100mm; the step delineates the messy lower stuff which gets water & dirt splashed on it, and the higher up cleaner stuff. The foamed glass is easy to use, easy to fit nicely to slightly uneven bits of wall - just grind it a bit against the wall, and it'll fit anything perfectly!
I did perimeter because it would have been a huge disturbance to dig out the floors. Really not that SWMBO friendly!